1. Field of the Invention
The present invention relates to a numerical control device which is provided with a heat radiation characteristic estimation part. The present invention more particularly relates to a numerical control device in a motor drive system which is provided with a cooling device and drives at least one motor using such a numerical control device wherein the numerical control device is provided with a heat radiation characteristic estimation part which can discover abnormalities in a cooling device of a component element which forms a portion of a motor part of the motor drive system.
2. Description of the Related Art
A machine tool system has a motor for each drive shaft of the machine tool and drives these motors by a motor drive system. The motor drive system is provided with a motor part and a numerical control device which controls the motor part. The motors in the motor part are controlled by the numerical control device by numerical values. Further, the operations of the motors are monitored by the numerical control device of the motor drive system. Further, the motor part of the motor drive system is provided with an input power source, converter, and inverters for making the motors operate.
On the other hand, in the motor part of a motor drive system in which a converter or inverter is used to control a motor, the heat generated by the converter or inverter and the heat generated by the motor cause the temperatures of the converter, inverter, and motor which form the motor part to rise. Further, if the temperatures of the converter, inverter, and motor rise, these component elements are damaged by heat and the motor drive system can no longer normally operate. For this reason, the converter, inverter, and motor are provided with a cooling device for preventing a temperature rise. The cooling device is generally an air-cooling type cooling device which uses cooling fins. In an air-cooling type cooling device, the cooling fan is driven by a fan motor to generate cooling air which cools the insides of the converter, inverter, and motor. Further, in such an air-cooling type cooling device, for preventive maintenance, a speed sensor which is attached to the fan motor is used to monitor for drop in speed of the fan or for the state where the fan stops and to prevent temperature rises in the converter, inverter, and motor.
In this regard, in such a method for preventing a rise in temperature, a speed sensor was separately required for detecting the rotational speed of the fan motor. On top of this, a temperature rise in the converter, inverter, and motor due to a drop in the cooling efficiency due to factors other than the drop in rotational speed of the fan motor could not be detected. On the other hand, in a control system using a motor, an overheating protection device for preventing overheating of the motor is disclosed in Japanese Patent Publication No. 2008-54440A. The device which is described in Japanese Patent Publication No. 2008-54440A is an overheating protection device in an electronic power steering system. This estimates the temperature from the heat generation characteristic and the heat radiation characteristic based on the difference in the heat capacities of several components (motor and controller) and limits the current which flows to the motor to protect the motor and the devices around the motor from overheating. Further, in the same field of numerical control devices, the art of increasing the acceleration/deceleration constant or decreasing the feed speed to prevent in advance overheating of the feed shaft motor of the machine tool to protect the machine when the amount of heat generated by the motor exceeds the allowable amount of heat generation is disclosed in Japanese Patent No. 3902710B2.
However, the control device of the motor which is disclosed in Japanese Patent Publication No. 2008-54440A estimates the temperature of the motor and the temperature of the motor controller from the difference between the amount of heat generated due to the motor current and the amount of heat radiated, so has the issue that since there is no temperature detector, it is not possible to precisely estimate the amount of heat radiated. Further, in the numerical control machine tool which is disclosed in Japanese Patent No. 3902710B2, operation of the driving means is suppressed when the allowable amount of heat generated which is determined by calculation of the temperature of the driving means from the current to the driving means or torque command data is exceeded by the total amount of heat generated which is found from operation based on the current to the driving means or torque command data. However, the numerical control machine tool which is disclosed in Japanese Patent No. 3902710B2 has no temperature detector, so there is the issue that it is not possible to precisely estimate the temperature of the driving means (heat radiation characteristic).